1. Field of the Invention
The present invention generally relates to plungers for use in gas-producing wells and, more particularly, is concerned with a flexible plunger apparatus designed for free movement in these wells.
2. Description of the Prior Art
Gas-producing wells typically employ a plunger disposed within a tubing of a well and capable of traveling vertically in the tubing as the well is cycled between shut-in and opened conditions in a manner wellknown to one of ordinary skill in the art. The plunger has been referred to as a "floating" or "free" plunger in U.S. Pat. No. 2,714,855 to Brown and as a "gas lift" plunger in U.S. Pat. No. 3,181,470 to Clingman in view that the plunger is freely movable vertically in the well tubing and is adapted to rise vertically under the force of sufficient gas pressure to drive or lift the plunger and a slug of liquid, such as oil, above it to the surface while isolating the base of the liquid slug from the gas which lifts the plunger. The plunger falls by gravity back down the tubing of the well after the slug of liquid has been delivered to the surface.
As shown in FIGS. 1 and 2, a typical prior art plunger P is a rigid inflexible device. The rigid plunger P has a rigid, non-flexible central rod R and a pair of end members E attached to opposite upper and lower ends of the rod R. Between the opposite ends of the rod R, the plunger P typically has a series of segments S, such as wobbly washers (see FIGS. 5 and 6), a brush (see FIGS. 9 and 10), expandable pads (see FIG. 11) or the like, applied over the rod R for creating with the interior surface of the tubing T a physical barrier or sliding seal to isolate the gas from the liquid slug and also for wiping parafin and the like from the inside wall of the tubing T. Gas pressure in the tubing T below the plunger P increases during well shut-in condition so as to cause lifting of the plunger P to the upper end of the tubing T when the well is opened. When the well is then returned to the shut-in condition, the plunger P due to the force of gravity falls to the lower end of the tubing T until the pressure of the gas has built up again. The purpose of the plunger P is generally two-fold: primarily, the plunger provides a physical barrier or moving seal between gas below and the slug of liquid above the plunger P for removal of the liquid slug which is forced from the tubing T when the well is opened; secondarily, the plunger wipes the interior surface of the tubing T in order to prevent build-up of parafin or the like thereon.
A growing number of gas-producing wells, however, use coiled flexible tubing. This tubing when uncoiled and inserted into the well bore tends to take on a helical or wavy curvature. There are other applications where portions of the well casing or tubing take on an angular condition. Prior art rigid plungers, being generally inflexible longitudinally or lengthwise, tend not to be able to negotiate the curvature of the tubing. Thus, a rigid plunger may bind up and become stalled, requiring the initiation of a time-consuming and costly fishing-out operation to be performed from the surface to remove the plunger.
Consequently, a need still exists for an apparatus which overcomes the aforementioned problem with prior art rigid plungers in gas-producing wells without introducing any new problems in place thereof.